This invention relates to a method and apparatus for processing a semiconductor workpiece.
Sputter deposition of metal films is widely used in the semiconductor and related industries. It is usually desirable to maximize the deposition rate of the sputtered film so that the number of wafers per hour that can be processed is as high as possible.
However, high deposition rate PVD (physical vapour deposition) processes present IC (integrated circuit) manufacturers with integration issues. As the power supplied to the sputter target increases so does the ability of the hot plasma and incoming energetic species to heat the wafer. For many applications it is necessary to keep the wafer temperature as low as possible to avoid affecting previously deposited materials that may be sensitive to elevated temperatures (e.g. polymers, adhesives, dielectrics, etc.).
One existing solution involves the processing of the wafer on a cold electrostatic chuck (ESC). At process pressure the thermal transfer between the wafer and the ESC is very low, (M. Klick, M. Bernt, JVAC 24 (2006)). The industry standard approach to improve thermal conductivity between the substrate and the chuck is to use a backside gas pressure. However, for thinned, highly warped, damaged, taped, or insulative wafers it can be very problematic to generate a clamping force that is sufficient to keep the wafer clamped during the deposition process when a gas back pressure is used. This type of problematic wafer is commonly encountered in the IC packaging industry. For example, it is common to utilise thinned wafers of thickness less than 100 microns, typically of 30-50 microns thickness. Wafers of this type are fragile, and can warp easily. A particular problem is encountered when a relatively thick layer of metal is deposited on the wafer. The metal layer is often 2-10 microns thick, which places an additional stress on a fragile wafer.